Switching power supply current sensing, zero-crossing detection and overvoltage protection

A control circuit for a switching power supply, the control circuit comprising:

• a) a sampling circuit configured to obtain an inductor current and a drain-source voltage of a main power transistor in a power stage circuit, in order to generate a sampling signal;
• b) wherein the control circuit generates an inductor current sampling signal according to the sampling signal during an on-period of the main power transistor,
• c) wherein during an off-period of the main power transistor, the control circuit generates a zero-crossing signal of the inductor current and an overvoltage signal of an output voltage of the switching power supply according to the sampling signal;
• and
• d) wherein the sampling circuit comprises a current sampling circuit configured to obtain the inductor current and generate the inductor current sampling signal, a differential circuit comprising a first capacitor and a third resistor, and being configured to generate a differential signal by differentiating the drain-source voltage when the main power transistor is turned off, and a voltage divider circuit configured to divide the drain-source voltage to obtain a voltage divider signal when the main power transistor is turned off.